Bibliographic details of references provided in the subject specification are listed at the end of the specification.
Reference to any prior art is not, and should not be taken as an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in any country.
Drug delivery systems aim to provide the required amount of drug systemically or to a targeted site for a time and under conditions sufficient to have the desired effect. Some drug delivery systems require carrier materials to mitigate particular undesirable properties of the drugs. One such type of carrier molecule is a cyclodextrin which acts as a host for a selected guest molecule.
Cyclodextrins are cyclic oligosaccharides with hydroxyl groups on their outer surface and a void central cavity which has a lipophilic character. Cyclodextrins are capable of forming inclusion complexes with hydrophobic molecules. The stability of the resulting host/guest complex depends on how readily the guest molecule occupies the central cavity of the host.
The most common cyclodextrins are α-, β- and γ-cyclodextrins consisting of 6, 7 and 8α-1,4-linked glucose units, respectively. Cyclodextrins have relatively low solubility in water and organic solvents and this limits their use in pharmaceutical formulations. For a description of the general chemistry of cyclodextrin, reference can be made to Fromming and Szejtlic (eds), Cyclodextrins in Pharmacy, Kluwer: Dordrecht, The Netherlands, 1994: Atwood, Davies, MacNicol and Vogtie (Eds), Comprehensive Supramolecular Chemistry Vol 4, Pergamon: Oxford UK, 1996; and Thomason, Crit. Rev Ther Drug Carrier Syst 14:1, 1997.
Alphaxalone [Alfaxalone or 3-α-hydroxy-5-α-,pregnan-11,20-dione] is a potent neuroactive steroid anaesthetic currently used in veterinary medicine (Child et al., British Journal of Anaesthesia 43:2-13, 1971).
Alphaxalone was widely used around the world as an intravenous anaesthetic together with alphadolone [Althesin; Alfathesin] in human patients until 1983. Although these anaesthetics have a high therapeutic index, they were nevertheless withdrawn from clinical practice due to occasional, unpredictable yet severe anaphylactoid reactions to a polyethoxylated castor oil excipient (Cremophor EL [Registered Trademark]).
Currently, a lipid formulation of di-isopropyl phenol (propofol) is the most highly used anaesthetic agent. Propofol, however, can be contraindicated in certain at risk patients due to its lowering effect on blood pressure, the effect it has on reducing cardiac output and it can adversely affect respiratory control. In particular, propofol is formulated in a lipid emulsion which can support microbial growth if contaminated. The formulation cannot, in fact, be sterilized. There have been instances where microbially contaminated propofol formulations have resulted in patients becoming infected. One other issue with the current propofol formulation is the pain induced following or during intravenous injection. Attempts to re-formulate in a water-based preparation have led to increased injection pain. Propofol also can lead to cardiovascular and respiratory depression and has a low therapeutic index of 5, i.e. only 5 times the normal anaesthetic dose can lead to death. Furthermore, the anaesthetic is incompatible with plastic storage containers and plastic syringes which complicates syringe delivery equipment which is frequently in standard use for intravenous anaesthesia and sedation. The drug can also cause hyperlipidaemia and can induce toxicity when used in a larger dose by infusion. This is particularly problematic in the intensive care setting.
A neuroactive steroid anaesthetic has the potential for being more efficacious with fewer side effects than propofol.
There is a need, therefore, to develop a suitable formulation to enable the use of a neuroactive steroid anaesthetic agent in subjects.